Registrations of current (location/routing/tracking) area are used to inform the cellular network where the mobile subscriber currently is attached. This information is used to limit the number of cells used for paging of the subscriber user equipment (UE). Without registrations all cells must be paged, the latter approach does not scale. On the other hand the registrations cause signaling load as well. This means that the network must be configured to balance between registration and paging load.
The 3rd Generation Partnership Project for Evolved Packet System (3GPP EPS or System Architecture Evolution/Long Term Evolution, SAE/LTE) system introduces the possibility to provide the user equipment with individual information (a so-called Tracking Area (TA) list which can include multiple tracking area identities (TAIs)) on when to register to the network. The network will page the user equipment in all the Tracking Areas that are on the TA list. Thus, as long as the user equipment moves between the Tracking Areas on the TA list, it does not need to notify the network of its new location (e.g. by performing a Tracking Area Update). Note that this list of TAIs is sometimes referred to as a TA list and sometimes referred to as a TAI list. A mobility management entity (MME) can allocate a new TA list to a user equipment in conjunction with some EMM (EPS Mobility Management) procedures like Attach, Tracking Area Update (TAU) and GUTI (Global Unique Temporary Identity) Reallocation. Note that although a GUTI Reallocation procedure normally is performed in conjunction with another mobility management procedure, e.g. as part of a TAU or Attach procedure, it can in principle be performed any time while the user equipment is in EMM-REGISTERED state (i.e. when there is an EMM context in the UE). This means that an MME may allocate a new TA list to a user equipment any time while the user equipment is in EMM-REGISTERED state.
Too much signaling, both for registrations (tracking area updates) and paging causes system signaling load. Therefore, there is a need for finding solutions to reduce the signaling load in the network. If the signaling load is reduced also cost for network nodes are reduced.